Fluid pumps are used in a wide range of applications to move fluids (typically liquids) from a liquid storage tank to an inlet, or from a liquid reservoir to an outlet. One example application is in air conditioning systems.
Air conditioning systems are used to cool air by passing warm air through a heat exchanger, where the warm air comes into thermal contact with a cooler body, such as low pressure refrigerant fluid flowing through a pipe. As the air passes through the heat exchanger, thermal energy from the warm air is transferred to the cooler refrigerant fluid, cooling the air temperature and warming the refrigerant. As the air cools, the vapour pressure of the water constituent in the air reduces, and some of the water vapour condenses out of the air as water droplets. Typically, these condensed water drops first nucleate on the refrigerant pipes in the heat exchanger before running off the refrigerant pipe and collecting into a water reservoir.
In most household or small building installations of air conditioning systems, an outlet is provided from a bottom of the water reservoir to a lower point on an outside of the building. The water runs from the water reservoir to the outside of the building under the action of gravity, where it can enter the normal drainage systems also used for, for example, rainwater.
In larger buildings, it can be efficient to process multiple sources of waste water together or to reuse waste water in other systems within the building. This may require that the condensed water in the reservoir is transported to a liquid outlet at a higher point in the building. The water can be transported by pumping from the reservoir to the liquid outlet.
The flow rate of water into the reservoir of an air conditioning system is typically very low. For this reason, existing systems use a small reciprocating pump to transport the water from the reservoir to the liquid outlet. Even the small pumps typically have a pumping rate much greater than the flow rate of water into the reservoir. The lifetime of the pump may be significantly reduced or the pump may not work at all, should the pump be pumping air after all the water has been pumped from the reservoir. Therefore, the pumps are run only when required to clear the water from the reservoir. Between the outlet of the reservoir and the pump, there is a small filling chamber with a float switch. When the chamber is empty, the float is at a bottom of the chamber. As water passes from the outlet of the reservoir into the chamber, the water level in the chamber rises with the float on the surface of the water. A first switch operates at a predetermined filling level of the chamber to turn the pump on. When the water level drops significantly below this level, the pump will turn off. In order for the float switch to work correctly, it must be mounted at a precise angle, such that a guide rail over which the float travels is perpendicular to the surface of the water. An air inlet to the chamber is also required to allow trapped air to escape as the chamber fills with water. In some systems, a second switch is provided which is operated when the float is near to a top of the chamber, indicating the chamber is almost entirely filled with water. In the situation where there is a problem with the pump, this second switch serves as a safety mechanism which will shut down the air conditioning system, preventing water continually entering the chamber and the reservoir overflowing. The second switch is also operated if the air conditioning unit is generating a flow rate of condensate which exceeds the pumping capacity of the pump.
It is typically difficult to install the filling chambers in the correct orientation as many may be hidden behind the main air conditioning unit. If the unit is not installed in the correct orientation, the float switch may not work correctly, or at all. In some situations, the float may get stuck at the top of the chamber, even when the pump has operated to pump water from the outlet of the reservoir to the liquid outlet. In this situation, the pump will continue pumping, and may start to pump air, resulting in damage to the pump, or even to failure of the pump. The pump may also or instead generate excessive noise.
The present invention, at least in some embodiments, attempts to provide an alternative to fill level sensors of the prior art.